Supplemental Cash Flow Information - Narrative (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Transfer from Investments	$ 187	$ 78
Non-cash financing activities related to the issuance of shares for vested restricted stock units	48	$ 30
Operating lease, payments	115
ROU asset obtained in exchange for operating lease liability	534
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
ROU asset obtained in exchange for operating lease liability	$ 488